CAS : arbitrary precision integer and floats, integer and polynomial arithmetic (gcd, extended gcd, factorisation, …), simplification, equation solver, partial fraction decomposition, calculus (derivation, integration, limit, series expansion), linear algebra (vectors, matrices, row reduction to echelon form, eignevalues and eigenvectors), …
geometry(2-d and 3-d) : point, segment, line, plan, triangle, polygons, circles, conics, parametric curves, surfaces, intersection, tangents… Dynamic 2-d geometry. All geometric instructions are programmable
Spreadsheet : relative and absolute references, cells can contain formal objects (e.g 1/2, sin(x), …), 1-d and 2-d statistics (mean, stddev, hgistogram, covariance, regressions, …)
Programmation : functions, local variables, tests, loops. Choice of syntax (C-like, Maple, Mupad, TI89). It is sometimes possible to run a Maple, MuPAD or TI89 without user intervention inside Xcas. Program editor. Interactive debugguer.